Studies of cigarette smoking have largely focused on adults, but the majority of smoking begins during adolescence. Nevertheless, comparatively little research has focused on adolescent smoking, and still less work has attempted to determine the genetic and environmental factors contributing to smoking initiation and persistence. The purpose of the current proposal is to examine the development of cigarette smoking in a large sample of twins representing the adolescent period of development. The Minnesota Twin Family Study (MTFS) is a longitudinal study of 1,300 twin pairs born in Minnesota between 1971 and 1981 and their families. Our goal is to apply existing behavior genetic methodology (Hannah, Hopper, & Mathews, 1985; Heath, 1990; Neals & Cardon, 1992) to examine the process of becoming a dependent smoker. The present study will apply existing models for smoking initiation and persistence, examine which environmental variables (e.g., peer pressure to smoke, availability of cigarettes) are most associated with smoking initiation, and model the progression to nicotine dependence with this existing data set. The results of these analyses will help inform the interventions that will be considered for Dr. Harry Lando's "Modifiable Factors in Adolescent Smoking" studies.